Electronic photocontrols are used to automatically turn on lights, such as street lights, parking and sales lot lights, barn lights, flood lights, and billboard lights, when it gets dark, and off when it gets light. See, for example, U.S. Pat. No. 5,195,016 incorporated herein by this reference.
For other lights, such as subway entrance lights, tunnel lights, and for devices such as golf course fountains and the like, the reverse is true: they must automatically turn on in the daytime and turn off at night.
In many cases, however, it is desirable that the lights or devices do not stay on all night or all day. For example, to save energy, every other street light or groups of parking lot lights may be turned off halfway through the night, at approximately midnight, when pedestrian and vehicular traffic is at a minimum.
And, for billboard lights, there is often a desire to turn the lights on when it gets dark, off some time during the night to save energy, and then on again during the rush hour traffic commute if it is still dark (called the "A.M. burn" in the trade) and then off again when it gets light.
A few prior art photocontrols accomplish these tasks either mechanically or electronically through the use of a settable timer. See, for example, the "Light Master" specification by Area Lighting Research, Inc.
The problem with mechanical systems is their inherent unreliability and complexity involving numerous gears and cams. If such a controller fails with the light on, there is a tremendous waste of electricity. In addition, the replacement labor cost as a consequence of a failure greatly exceeds the cost of the controller itself.
The problems with electronic timer based systems which must be set before use are numerous. First, such systems typically include batteries which can fail or degrade in harsh climates. Second, once the timer is set, it does not take into account the longer winter nights and the shorter summer nights especially at extreme latitudes. Adjusting the setting is cost prohibitive. Third, different settings may be required at the factory depending on where the controller will be installed since midnight in California is different than midnight in Massachusetts. This labor intensive setting procedure is also cost prohibitive. Fourth, previous designs and systems were expensive. Finally, power outages and failures can severely affect the factory settings and again, the user incurs excessive adjustment labor costs.